72 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
shining, smooth, thick, dark brown; young shells typically modiolaraeform, 
umbos directed anteriorly; anterior dorsal margin slightly crenulated; 
adult shell with dorsal and ventral margins nearly parallel; anterior and 
posterior margins rounded; umbos worn, not conspicuous, situated 
about % the distance from the anterior to the posterior extremity; incrusta¬ 
tion thin, porous, covering the posterior area diagonally, prolonged beyond 
the valves; internal ligament prolonged posteriorly; inner surface pale; 
posterior adductor scar large, circular, impressed; with a sub-umbonial 
callosity, conspicuous toward the pedal scar. Length, 40; height, 10; 
diameter, 11 mm. (Philippi.) 
Type. Location of the type not known to the writer. Type locality, 
Vancouver Island. 
Range. Vancouver Island to San Diego, California. Also North 
Japan. 
Genus DACRYDIUM Torell, 1857. 
Hinge crenulations tuberculiform anteriorly, elongate posteriorly. 
(Tryon. S. S. Conch.) 
Type. D. vitrea Sars. 
Dacrydium pacificum Dali, 1916. 
Proc. U. S. N. M., 52 :405. 
Shell minute, whitish, much the shape of Modiolaria vernicosa Midd. 
on a minute scale, differing from the Atlantic D. vitreum by its smaller 
size and more elongate outline. Length, 3.6; height, 2.5; diameter, 1.5 
mm. (Dali.) 
Type in U. S. N. M., No. 214092. Type locality, Station 3604, Bering 
Sea, in 1401 fathoms. 
Range. Known only from the type locality. 
Genus LITHOPHAGA Bolten, 1798. 
Shell cylindrical, inflated in front, wedge-shaped behind; epidermis 
thick and dark; interior nacreous. 
The “date shell” bores into corals, shells, and the hardest limestone 
rocks. (Tryon. S. S. Conch.) 
Type. MytUus lithopJiagus Linnaeus (in part.) 
Distribution. West Indies, New Zealand, United States, Japan. 
Range in time. In the Carboniferous of Europe and the United 
States. 
